Incidental thyroid carcinoma identified by positron emission tomography scanning obtained for metastatic evaluation

Positron emission tomography (PET) scanning is an emerging technology with substantial implications for patients with solid tumors. PET is useful in identifying sites of metastatic disease as well as primary malignancy and evaluating suspicious findings found via other imaging modalities. PET is becoming a standard modality for metastatic evaluation of a variety of malignancies. However, this imaging is not limited by histology and may reveal clinically occult second lesions. We present five cases of a clinically occult thyroid cancer found in patients who underwent PET scanning for metastatic evaluations. The principal diagnoses included two patients with malignant melanoma, one each with gastric, rectal, and colonic adenocarcinoma. None of the cases had findings on physical examination. Increased uptake in the region of the thyroid was evident on the PET scan, and fine-needle aspiration biopsy indicated papillary carcinoma of the thyroid in all five cases. Although evaluation of metastatic disease is the primary purpose for PET in this setting the discovery of occult thyroid malignancy is an additional benefit of such imaging. This emphasizes the importance of investigating suspicious areas found by PET and not simply assuming that these are all sites of metastatic disease. Furthermore incidental findings of uptake in the region of the thyroid make consideration of a primary carcinoma mandatory.